Authors:Łukasz Komsta, Urszula Dunin and Robert Skibiński
During our previous studies, we discovered that reversed-phase thin-layer chromatography (RP-TLC) plates can behave in typical normal-phase manner, which is not widely known nor used in the literature. Therefore, we decided to investigate this behavior more comprehensively on RP-8 plates. We used 35 model compounds, and performed chemometric screening mixture design approach for 20 popular solvents. This gave us the possibility to estimate separate retention effect for each solvent being the measure of average solvent strength. The results were compared to the previous study done on silica gel. It can be concluded that RP-8 plates can be used in typical normal-phase systems and their behavior does not differ substantially from silica gel plates.
Authors:Łukasz Komsta, Robert Skibiński, Sebastian Gadowski, Joanna Wróbel and Karolina Skrzypiec
The eluotropic strength on RP2 and RP8 plates was investigated for 7 chromatographic grade solvents miscible with water as a diluent (acetone, acetonitrile, dioxane, ethanol, isopropanol, methanol, and tetrahydrofuran) as well as for water itself. Thirty-five model compounds were used as a test set in the investigation. The use of a modern chemometric mixture design concept allowed separate estimation of each solvent effect from the other results with a relatively small error (about 0.05 of RM value for both adsorbents). Principal component analysis was used as an additional tool and revealed that only one parameter (mean eluotropic strength) is satisfactory to explain the overall variability in the retention datasets. The bootstrapping approach was also used to check the distribution and uncertainty of the obtained values. It can be concluded that all solvents have quite similar elution strength for both adsorbents. The obtained values can be used as a reference during the optimization of thin-layer chromatography (TLC) systems.
Authors:Ádám Dávid, Emil Mincsovics, István Antal, Éva Furdyga, Zsolt Zsigmond and Imre Klebovich
We report a new combination of overpressured-layer chromatography (OPLC) with near-infrared (NIR) spectroscopy for pharmaceutical analysis. Different pharmaceutical preparations containing caffeine, paracetamol, and acetylsalicylic acid as model compounds were separated by OPLC. The band density in the solid phase after OPLC was suitable for study of the separated components directly on the layer by NIR spectroscopy.We have demonstrated the applicability of rapid OPLC separation combined with UV densitometry and NIR spectroscopy for both qualitative and quantitative analysis. This OPLC-UV-NIR technique is thus suitable for rapid, nondestructive investigation of multicomponent pharmaceutical preparations and enables a different type of pharmaceutical analysis, e.g. starting-material tests, in-process control, end-product control, stability testing, etc. Another benefit of this newly developed combination of rapid off-line techniques is the possibility of simultaneous collection of qualitative and quantitative chromatographic and spectral information.
Authors:Ana Reverdito, Mariano García, Alejandra Salerno, Oscar Locani and Isabel Perillo
When the components of a reaction mixture cannot be quantified by UV-visible spectrophotometry, because the
values of their absorption bands overlap, the components can be separated and quantified by spectrodensitometric thin-layer chromatography (SDTLC). In this work an aminolysis reaction mixture in aqueous medium was studied by TLC on silica gel plates with densitometric detection. The reaction, an intramolecular rearrangement involving migration of an acyl group, was studied by monitoring a carbinolamine intermediate for which
was identical with those of the substrate and product. SDTLC not only enabled detection of all three components of the mixture when the plate was developed but also enabled detection of covalent and ionic forms of the reaction intermediate by comparison of their absorbance/reflectance spectra with those of structurally related imidazolidine and amidinium salt derivatives, respectively, used as model compounds. Kinetic studies, among others, may also be performed by SDTLC to determine the mechanism of the reaction.
In this work an attempt is made to have a closer look at technetium species (TcX) induced by spinach plants, grown on TcO
containing nutrient solutions. To this end, size-exclusion chromatography (SEC) and reversed-phase ion-pair chromatography
(RP-IPC) were used: The performance was established with model compounds, i.e., anionic Tc-DTPA and cationic Tc-cyclam, used
as mimics for TcX. Under the conditions applied, the information retrieved from high performance RP-IPC was minimal due to
strong interactions of the technetium species with the Nucleosil C18 stationary phase. However, in low-pressure SEC non-size
effects allowed differentiation of TcX into two distinct classes of technetium compounds, i.e., TcX1 and TcX2. From retention behavior in SEC, it was possible to speculate on the chemical properties of these two technetium species.
Authors:Miha Vivoda, Robert Roškar and Vojko Kmetec
This study presents a contribution in the development of a quick and accurate testing method for the determination of amorphous content using isothermal microcalorimetry. Examples demonstrated how the choice of the experimental conditions, especially sample load, temperature and humidity, influences the crystallization of the amorphous material. The suitability of this systematic approach was first tested on well-known lactose and afterwards on nifedipine as model compounds. It was shown that by proper method design and careful selection of experimental conditions, it is possible to achieve quick determination of the amorphous content in samples with a quantification limit of less than 1%, what is considerably better than by classical analytical methods such as DSC and XRPD. Our optimized microcalorimetry method gave also better results compared to previously reported literature data for nifedipine.
Vanilla bean is a valuable food additive used in many branches of food industry as a source of natural vanillin. The influence of60Co -radiation in the dose range of 5–50 kGy has been investigated on: (1) the survival of contaminating microflora, and (2) more important vanilla constituents like vanillin and sugars. It has been found that the main vanilla contamination is connected with mesophylic microorganisms in the amount of 8.4·104/g. The dose of 15 kGy is sufficient for decontamination of commercial raw material. The samples under investigation on account of sensory properties and chemical composition were in agreement with country regulations. Doses up to 50 kGy do not cause undesirable changes in the content of sugars and vanillin, which has been confirmed by studies on model compounds.
We have recently described a rapid non-synthetic method for producing14C-and11C-labelled biomolecules. The apparatus consists of a high vacuum system in which small amounts of14CO gas are ionized by electron impact. The resulting ionized, excited and dissociated species drift toward a thin layer of
organic molecules where they interact to produce14C-labelled compounds. In this paper, details are given on the mechanisms of interaction of the electron beam and on the parameters
influencing the labelling yields. Using cholesterol as a model compound labelling yields were measured while the electron
energy, thickness of the organic film, gas pressure and time of exposure were varied over a wide range. The results suggest
that14C+ and/or14CO+ are the principal species involved in the labelling reactions.
Solution heats in chloroform at 25 C have been measured experimentally for poly(methylmethacrylate) (PMMA), samples of poly(styrene-co-acrylonitrile)
(SAN) containing from 5 to 37 mass% of acrylonitrile, and some PMMA-SAN blends prepared inside the miscibility range. From
these data the mixing enthalpies for blend formation were obtained. Use of the mixing heats values in the framework of the
Prigogine-Flory-Patterson theory allowed to calculate values of the exchange energy parameters between the components of the
blends much more negative than existing literature data. Calculation of binary interaction energy parameters between the single
repeat units of the copolymer from the above data, and from model compounds, clearly indicates a strong increase of the intramolecular
repulsive energy between nitrile and styrene units of SAN, as compared with the interaction between the corresponding free
Authors:J. Kučerík, D. Kamenářová, D. Válková, M. Pekař and J. Kislinger
DTA/TG technique has been used to study the influence of various model compounds
(aromatics, organic acids, alkanes, ketone, heterocyclic and sterole) on the
thermo-oxidative behavior of lignite humic acids. As a measure of stability
the shift of the onset temperature of the exothermic degradation peak has
been used. Further, the ratio of mass loss recorded in the high and low temperature
ranges (thermogravimetric index) was used to evaluate the role of added compounds
on the recombination reactions occurring during the thermooxidative degradation
of humic acids. It has been demonstrated that most of added compounds play
a role during those processes at relatively low concentrations (1% mass/mass)
and affect the humic acid stability as well as the value of thermogravimetric
index (i.e. the degree of the apparent aromaticity). It has been clearly shown,
that the latter parameter reflects more the ‘qualitative’ than
the ‘quantitative’ relationship between biodegradable humified
parts in the extracted pool of organic matter.